An aftercooler for cooling a compressed fluid exiting from a compressor, the aftercooler including a radiator unit for receiving the compressed fluid exiting from the compressor and for cooling the compressed fluid, the radiator unit having an inlet for receiving the compressed fluid, an outlet for discharging the compressed fluid and a plurality of heat exchange passageways connecting the inlet and the outlet for transferring heat from the compressed fluid. The aftercooler also includes a bypass channel for bypassing the plurality of heat exchange passageways which extends from a first point substantially adjacent the inlet of the radiator unit to a second point substantially adjacent the outlet of the radiator unit.